If a surface of a substrate such as a steel plate is coated with a thin film using plasma, a stratum tectorium having good consistency and abrasion resistance is formed. Products having the stratum tectorium are used as a magnetic disk, optical disk, carbide tool and the like. Also, if the paint-coated film generated on the surface of a steel plate is undergone plasma processing, an unplasticized paint which coated steel plate having good durability and corrosion resistance. Particularly, through the processing, quality of the surfaces can be improved increasing hydrophile and hydrophobe by polymer polymerizing the surface of the substrate, and the improved substances are widely in use.
As a typical example of the plasma polymerizing apparatus, an apparatus is disclosed in WO99/28530. In FIG. 1, the apparatus is composed of a vacuum chamber 1, and electrode 4 installed in the chamber vacuum pumps 5, 6 for controlling pressure in the vacuum chamber, gauges 7, 8 for measuring degree of vacuum, a power supply apparatus 3 for generating potential difference in an electrode, and reactive gas adjusting apparatuses 9, 10 for supplying unreactive gas such as reactive gas and nitrogen around the substrate.
An example of plasma polymerizing processing by the above apparatus will be described as follows. The substrate 2 is installed in the chamber 1 and whether the pressure in the chamber is maintained to be vacuous about 10−6 Torr is checked with the ion gauge 8 by starting the diffusion pump 6 after checking whether the pressure in the chamber is maintained to be vacuous about 10−3 Torr with the thermocouple gauge 7 by starting the rotary pump 5. The substrate is biased-positioned as an anode (or an active electrode) by the power supply 3 and the electrode 4 on the other side is grounded. If the pressure of the chamber is maintained as regular vacuum, reactive gas and unreactive gas are supplied around favorable places in order. The mixture ratio is controlled by the pressure of the thermocouple measurer. In case the pressure in the vacuum chamber become a certain vacuum, the vacuum chamber is discharged with direct current or high-frequency wave. Then, in the plasma generated by the direct current or high-frequency wave, the molecular binding is broken and the broken chains and activated cation and anion combine, thus to form a polymerized material on the surface of the substrate which is positioned between the electrodes.
In the above apparatus, a power is not supplied to the electrode 4 and is grounded. In case a power is supplied to the electrode, the electrode is needed to be insulated with the chamber and a means for fixing the electrode is needed to position the substrate to have a predetermined interval from the processed substrate. Particularly, in case of an apparatus capable of continuously performing plasma polymerizing processing as well as the above discontinuous apparatus, when the apparatus is operated for a long time, the electrode can be slack down or the interval between the electrode and the substrate can be changed.